Memory and Storage: RAM, ROM and the Backing Store
Ordinary RAM holds working instructions and data and loses them without power. ROM retains firmware. Secondary storage keeps saved files between runs, but devices can fail. Compare capacity, access time, cost and physical risks for a stated use.
What a learner can do afterwards
- Distinguish what ordinary RAM, ROM and secondary storage retain without power
- Explain why a typical desktop application loads needed instructions into RAM and saves lasting data to storage
- Compare stated drive characteristics and calculate backup capacity under stated assumptions
1 · Read
Ordinary RAM is volatile: it needs power to retain working instructions and data. ROM is nonvolatile memory used for firmware, the low-level instructions that help a device start. Some firmware memory can be updated through a special process. ROM is not the usual place to save changing documents.
Restarting ends processes and starts the operating system again. It can release RAM held by unneeded processes or a program that keeps allocating unused memory. It does not fix every cause of slowness. Startup processes may return. Save work first; programs can write files during shutdown.
A typical desktop application loads needed instructions and working data from storage into RAM. The CPU accesses them through the memory system, often using caches. This provides fast access during execution. Not every device works this way: some execute firmware directly from ROM.
Working data belonging to a process is not a lasting save. Saving writes a version to persistent storage for later runs. If a change exists only in RAM, with no autosave or recovery copy, it is lost in a power failure. An older saved file can remain. Nonvolatile storage can still fail, so saving and backing up protect against different risks.
HDDs use moving magnetic parts. SSDs use flash memory with no moving parts and usually have shorter access times. HDDs often cost less per gigabyte at high capacities, but compare actual models and prices. An SSD avoids some mechanical damage risks during a knock; either drive can fail. Choose using the stated capacity, cost, access time and physical risks.
Keep a backup on separate storage and check that you can restore it. Space needed depends on file sizes, retained versions, compression and overhead. There is no universal twice-the-drive-size rule. For one uncompressed copy with no overhead, add all the file sizes: 250 GB plus 50 GB requires 300 GB free.
RAM is volatile; ROM and drives retain data without power. Save changes and keep a separate backup that you can restore.
Lesson, worked questions and flashcards about RAM, ROM and saved files were written for this dataset.
Five readings and six flashcards about memory, saved versions, backups and drive comparisons were written for this dataset.
More to read
Retention is not a guarantee against loss
A computer can retain a saved file while switched off. HDDs use magnetic storage; SSDs, USB flash drives and many memory cards use flash memory. These are examples of secondary storage.
Ordinary RAM has a different role. It holds working instructions and data and needs power to retain them. ROM is also memory, but it is nonvolatile and normally holds firmware. The word memory alone therefore does not tell you whether contents survive without power.
Nonvolatile does not mean indestructible. A stored file can become unavailable if its device fails, is damaged or is lost. A separate backup provides another copy; persistence alone does not.
A saved version and a working version
A drawing app can read a saved picture and let you change it. The app keeps working data while you edit. The stored file need not change after every brush stroke.
Saving writes a version to persistent storage. Another run can read it into new working data. Ending the current process does not automatically save its variables.
If power fails, edits held only in ordinary RAM are lost. A saved version may remain on an undamaged drive. Autosave or recovery files can preserve other versions, so check what the app actually stored before deciding what was lost.
Choose backup space from the backup plan
List the files you need to recover and check their combined size. Then check whether the backup retains older versions, compresses files or adds storage overhead. Those choices affect its capacity requirement.
A second folder or partition on the same physical drive does not protect against that drive failing. Keep another copy on separate storage. Separate storage can also be lost or damaged, so it is not failure-proof.
Test the backup by restoring a sample file and opening it. Update the copy as your work changes. A readable but outdated backup may still lack the work you need.
Why a restart sometimes helps
Running programs compete for RAM and other resources. An unneeded process can hold memory that other work could use. A program may also keep allocating memory it no longer needs.
Restarting ends processes and starts the operating system again. That can remove a temporary cause of poor performance. Programs set to start at boot may return, and hardware or storage problems do not disappear just because processes restart.
Save your work first. A normal restart does not erase all saved files, but programs may write files while shutting down. An improvement after restarting is useful evidence, not proof of one particular cause.
Match drive ratings to the job
An archive needs enough capacity for its files. A task that repeatedly requests small pieces of data also depends on access time. Cost per gigabyte and access time answer different questions.
HDDs contain moving magnetic parts. SSDs use flash memory without a moving read head. SSDs usually have shorter access times, while HDDs often offer lower cost per gigabyte at high capacities. Use actual specifications and prices rather than assuming one device wins every comparison.
No moving parts removes some mechanical risks, not every failure risk. Whichever drive you choose, keep a separate backup. This comparison does not provide instructions for installing or formatting hardware.
2 · Watch
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.