Page 57 - UNI 101 Computer Science Handout.

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where traditional ROM would be impractical. Whereas traditional ROM must be read, erased, and

written in large blocks of addresses, it is possible to read individual bytes or small blocks of flash memory

when necessary.

This makes flash memory useful for applications that require random access, particularly those

applications where most accesses are reads. Although read accesses and certain simple overwrite

accesses are relatively fast, flash memory must be erased in blocks, so that most write accesses require

an additional step that rewrites the unchanged data back to the block. Furthermore, the erase-and-
rewrite operation is very slow compared to the read access.

Although there is research into other types of nonvolatile memory that might solve this problem, flash

memory is generally considered to be impractical as a replacement for conventional RAM, at least for

now. Because of its small size, flash memory is frequently the secondary storage of choice for the
memory cards that plug into portable devices such as cell phones, portable music players, and digital

cameras. It is also well suited for small, portable ‘‘thumb drives’’ that plug directly into a USB port. These

drives are useful for moving files and data from one machine to another and also serve as an inexpensive
and convenient backup medium. Flash memory is more expensive than disk storage at this writing.

However, its capacity is rapidly increasing and its price falling.

As a result, large capacity flash memory units called ‘‘solid-state drives’’ have appeared on the market

and are starting to supplant disk drives as the long-term storage device of choice in computers where
less weight, low power consumption, and small size are important. ‘‘Solid-state drives’’ have the

additional advantages of being relatively immune to failure due to physical shock and vibration (since

they have no moving parts), and generate little heat and no noise. Solid-state drives have not yet reached

the huge storage capacities of large disk drives, but their capacity is continually expanding, and is already

adequate for many applications.

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57 Academic Year 2025/2026