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Would this make the term 'disk drive' a slight misnomer?

Also, I thought RAM was equivalent to the term 'volatile' memory, but apprently 'hard disk drives' are also RAM and not ROM... any clarification is appreciated!

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4 Answers 4

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Yeah, the terms have become a bit messy.

The term "drive" originally referred to the thing moving the storage media - like a floppy drive is something you put a floppy disk into and it spins it. A tape drive is the thing that drives the tape around the read-write heads. Originally with a hard disk, the drive was separate from the disk platters - you used to load the hard disk into the disk drive. Now, the drive is built-in. So a hard disk drive is referring to both the disk and the drive at the same time.

Now we have "solid state drive" or "solid state disk" which contains no drives and no disks.

These are storage media, ie where you keep applications and files.

RAM is volatile memory (usually) and where an application or the OS is loaded in order to run it. It is based on silicon chips rather than magnetic media.

A hard disk would never be referred to as RAM. The only time these two ideas get close is where an operating system might pretend it has extra RAM than it really does by using part of the hard disk as "swap" or virtual ram. Basically, the OS will swap unused contents of RAM to disk to free memoryfor other applications, then swap them back again when they are needed.

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  • Or when you're using a RAM-based SSD. Sep 30, 2011 at 4:16
  • Of course, hard drives might also contain volatile memory used for caching data to be read or written, as well as ROM chips with drive firmware.
    – user55325
    Sep 30, 2011 at 4:16
  • I can't wait for the day where RAM has a little hard disk in it that it backs itself up to when it senses power loss.
    – Paul
    Sep 30, 2011 at 5:34
  • Of course, the original RAM was core memory, which was magnetic media. Nov 16, 2016 at 2:45
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Would this make the term 'disk drive' a slight misnomer?

Since there is a (bad) tendency to shorten "adjective noun" names to just the "adjective" (e.g. "remote control" becomes "remote", "IP address" is "IP", "passive cooling" is "passive"), the term "disk" is often just short for "disk drive".

"Drive" used to be synonymous with "transport", the electromechanical device that would rotate/spin and read/write the media. Magnetic tape drives and disk drives are two types of transports.

The disk drives were as large as a washing-machine, had a hefty motor and read/write electronics, and used large (14") removable, multi-platter disk packs, aka "storage modules". The concept of mounting a filesystem comes from the physical act of mounting (installing) a disk pack in a drive.

The IBM Winchester disk was the first disk pack to incorporate the R/W reads with the disk pack (instead of part of the disk drive). The trend away from removable disk platters to fixed platters within the drive was under way with 8" hard drives. PC users only know of hard drives with fixed (non-removable) platters. Hence the terms "disk" and "drive" have evolved in to equivalent terms. In addition, a disk's attribute of storing a large amount of data leads to hijacking of the term for other mass-storage media such as "RAM disk" and "solid-state disk".

Also, I thought RAM was equivalent to the term 'volatile' memory

RAM is the acronym for random access memory. There is no assumption or characterization about volatility. In fact, if you're old enough to remember, computers (but not PCs) up to the 1980s used (non-volatile) ferrite core memory. Battery-backed static RAM is another way to implement main memory that is non-volatile. It's the (now prevalent) use of dynamic RAM for main memory and its attribute of volatility that leads to the faulty association of RAM and volatility.

  • RAM is (commonly) implemented by dynamic RAM.
  • DRAM is volatile.
  • Therefore RAM is volatile. Improper (if not faulty) syllogism!

apprently 'hard disk drives' are also RAM and not ROM

These are not the same devices. RAM and ROM are memories which are usually connected to the processor by an address and data bus. A hard disk drive is a peripheral which has the function of providing mass storage; it is addressed and performs data transfers in blocks (aka sectors).

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  • Isn't the hard disk drive also a kind of memory? Since it stores data...
    – Juan Perez
    Jun 6, 2023 at 15:16
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    @JuanPerez -- If you choose to use ambiguous definitions, then yes, you could conflate mass storage (like HDDs) with "memory". But that also indicates a lack of understanding about computer architecture. RAM can be accessed by the CPU with just one instruction. An HDD requires hundreds of instructions to initiate a sector read, and then hundreds more to receive and handle the sector. The differences are enormous and obvious once you get past these super-broad categories/labels that you're trying to apply.
    – sawdust
    Jun 6, 2023 at 19:12
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A Disk Drive is a combination of magnetic disks in a case referred to as a drive. Conceptually you can have 30 disks in one drive. So the point being here is that a disk is a magnetic round platter that is contained within a drive.

If you extend this analogy further a drive is the container, and the individual disk is one layer within that container. If you have one drive you can mount it and have different disks on that same drive. As an example, you could partition your drive :) - which is really just dividing up the disks differently - so that you have individual sections.

So they're not really redundant.

A Solid State Drive is a Solid State Container for Mass Storage - no disks, but you do have a container for that. Also, you want to mount your drive first before you mount individual disks or in the case of SSD, mounting the mass storage within the container, but the driver that enables the operating system to connect is talking to the drive, and not the individual disks/mass storage. Which is often the reason why you can access stored data even though the drive is busted.

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Terminology expands as new technology is developed, which may be confusing and usually needs adaptation. Here is a short terminology on computer storage:

primary storage (a.k.a. main memory, internal memory, memory) is the only memory directly accessible by the CPU. The three kinds of primary storage, from the fastest to the slowest, are: CPU registers, CPU cache, and RAM (random-access memory). The term random-access in the computer storage context refers to the characteristic of a storage device that individually addressable memory locations on the device can be accessed in any order equivalently in terms of time. Hard disk drives and solid-state drives are not primary but secondary storage devices, and they don't allow random access: Hard disk drives are mechanical storage devices that allow the data on the drive to be accessed at varying speeds depending on the location of the data on the surface of magnetic disks inside the drive assembly. And, even though solid-state drives aren't mechanical but purely electronic, they are still used as block devices, which means the drive doesn't allow the data stored on it to be accessed in random indvidual bytes of memory, but in blocks of memory, which is the main difference between solid-state drives and RAMs, and also SSD memory is much slower than RAM.

Secondary storage (a.k.a. external memory, auxiliary storage) is the memory that isn't internal to any peripheral device, and also not directly accessible by the CPU. Hard disk drives (HDDs) and solid-state drives (SSDs) are the most commonly used secondary storage devices.

Drive can be thought of as the short form of storage drive, and refers to to all secondary storage devices regardless of storage media they use. It is synonymous with storage device, which refers to only secondary storage devices since primary storage is the internal storage of the CPU. Drives can be movable or solid-state, internal or external, and physical or virtual. Therefore, the term includes hard disk drives (a.k.a. hard drives), solid-state drives, optical disc drives (CD/DVD/BD-ROM drives), floppy disk drives, USB flash drives and all other removable storage devices, network drives, and online storage services such as Google Drive. As for the usage of the terminology: a drive is partitioned; files are stored on, or written to a drive; and the bottleneck in performance is usually drive IO, also referred to as file IO. Microsoft's online style guide currently uses the term hard drive to refer to "a drive on a PC where programs are typically stored", which includes all secondary storage devices by definition, but hard drive is just short for hard disk drive, which is only one type of secondary storage devices. The term drive originally referred to an electromechanical device that was used to spin and read/write a storage medium mounted on it, e.g. spools of tapes used to be mounted on the motor spindle of furniture-sized tape drives, and floppy disks used to be inserted in floppy disk drives to mount the disk on the spindle. However, a modern storage device is a single unit that includes both the drive and the storage medium, and thus in addition to its original meaning, the term drive is now also used to refer to any storage device that replaced the drives of the past. The term drive capacity refers to the size of the storage medium in the drive.

Hard disk drive (HDD) (a.k.a. Hard drive, Hard disk) All three terms can be used to refer to a storage drive that uses magnetic disks as the storage medium, although the term hard disk or hard disk drive platter actually refers to one of multiple metal disks inside a hard disk drive assembly, which have magnetic surface coating where the data is stored. Hard disks are called hard in contrast with floppy disks that are flexible; "floppy" literally means limp (not stiff or firm) in English.

Solid-state drives (SSD) are called solid-state because all of the electrical activity in their circuitry occurs within solid materials (e.g. transistor, which is a solid-state device) unlike the technology they replaced, where the current flowed through thermionic vacuum tubes due to ion emission from heated electrodes. These are much faster than hard disk drives, especially the ones that use PCIe bus instead of SATA. AFAIK the NVMe host-controller interface is designed specifically for PCIe SSDs.

So, the terminology is complicated. As rarely as it is, even some documents from companies like Red Hat currently expand SSD as "solid-state disk", which is a misnomer since SSDs don't have disks, and a storage device with a disk wouldn't be solid-state unless disks weren't rotating. It also seems to be common to call SSDs hard drives, although this is a misnomer too since "hard drive" is just short for "hard disk drive", it's just a remnant of using disks for computer storage for so long, and the commonly used softare terms such as "disk partitioning", "disk benchmark", "disk mount", etc., which can use the term "drive" instead of "disk" to be agnostic to the storage medium. It also seems to be common that solid-state storage devices are thought to have no "drives" in them, that "they are not driven", although that's inaccurate since the drive is just not electromechanical but purely electronic (i.e. solid-state in modern technology): in the traditional sense of the term "drive", the memory controller, all other circuitry, and the firmware in SSDs is the "drive" that allows data stored on the storage medium, which is typically a flash memory, to be accessed.

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