Project PDA

Used for static memory on a PDA. Typically is space where Operating System is stored. Also Known As: Read Only Memory



Many microcontrollers include the program ROM, a CPU core, some on-board peripherals, and RAM, all on one chip. Practically all microprogrammed CPUs also include a kind of ROM on the same chip to hold the control store.

Home computers of the early 1980s came with their complete operating system in ROM, often including a BASIC programming language interpreter. There was no reasonable alternative because floppy disk drives were generally optional. Upgrading to a newer version meant replacing the old ROM chip with a new one -- using either a soldering iron or a set of DIP sockets.

By the 2000s, operating systems for desktop computers are not generally on ROM anymore. Computers may still rely on some software in ROMs, like their BIOS, but even that is more likely to reside on a Flash-ROM. Mobile phones and personal digital assistants are likely to have software in ROM (or at least flash memory).

Read-only memory (ROM) is used as a storage medium in PDA like computers. Because it cannot (easily) be written to, its main uses lie in the distribution of software that is very closely related to hardware, and not likely to need upgrading. For example, a networking or graphics card may implement some basic functionality through software contained on a ROM. ROMs typically take the shape of IC packages, i.e. black "computer chips", not immediately distinguishable from other chips like RAMs but for the text printed on the chips.

Nonvolatile memory read-only store in which all programs are essential to the PDA, such as your operating system. That is, the information contained in the ROM memory can not be changed and is permanent. However, if the memory is flash ROM, the operating system on the PDA can be updated.

Never store personal information in ROM (Read Only Memory). If you don't know what ROM is or how to get to it, you probably don't have access to it. If you do store personal infomation in ROM, even if your PDA is password protected, a hard reset can be done and your information will be available to whomever has your PDA.

One reason why some data still sits in ROMs is speed – disks are an order of magnitude slower. Even more important, though, is that you cannot read software that is needed to drive a disk from the disk itself. Hence the BIOS or a bootloader for a computer is often stored in ROM. Also, a networking or graphics card may implement some basic functionality through software contained on a ROM chip. Another application for ROMs is in storing software for embedded systems operating in physically demanding environments (exposed to, say, vibration, or high acceleration), where disks are too fragile.

Speed of ROMs:

Reading speed

Although this has varied over time, today, large RAMs can be read faster than most large ROMs. Therefore ROM content that is used often is sometimes copied to RAM and subsequently read from there (shadowed).

Writing speed

For those types of ROMs that can be written to or electrically altered, the writing speed is always much slower than the reading speed and it may require unusual voltages, the movement of jumper plugs to apply write-enable signals, and/or special lock/unlock command codes written to the EAROM/Flash ROM.