What is the ROM and in which sizes

ROM (Read Only Memory)

Read Only Memory (ROM) is computer memory that can permanently store data and applications within it. There are various types of ROM with names like EPROM (Erasable ROM) or EEPROM (Electrically Erasable ROM).

Unlike RAM, when a computer is powered down, the contents of the ROM are not lost. EPROM or EEPROM can have their contents rewritten by a special operation. This is called 'Flashing the EPROM' a term that came about because ultra violet light is used to clear the contents of the EPROM.

Size of ROM available

Macintosh Model	ROM Size
Macintosh 128	64K
Macintosh 512K	64K
Macintosh 512Ke	128K
Macintosh Plus	128K
Macintosh SE (both 800K & FDHD)	256K
Macintosh Classic (4-chip and 2-chip)	512K
Macintosh SE/30	256K
Macintosh Classic II	512K
Macintosh Color Classic	1024K
Macintosh II Models	ROM Size
Macintosh II	256K
Macintosh IIx	256K
Macintosh IIcx	256K
Macintosh IIci	512K
Macintosh IIfx	512K
Macintosh IIsi	512K
Macintosh IIvi/IIvx	1024K
Macintosh LC Models
Macintosh LC
Macintosh LC II	512K
Macintosh LC III	1024K
Macintosh LC 475	1024K
Macintosh LC 520/550	1024K
Macintosh LC 575	1024K
Macintosh LC 580	1024K
Macintosh LC 630	1024K
Macintosh TV	1024K
Macintosh Performa Models
Macintosh Performa 200	512K
Macintosh Performa 400/405/410/430	512K
Macintosh Performa 450/460/466/467	1024K
Macintosh Performa 475/476	1024K
Macintosh Performa 550/560	1024K
Macintosh Performa 575/577/578	1024K
Macintosh Performa 580	1024K
Macintosh Performa 600	1024K
Macintosh Performa 630/631/635/636/637/638/640	1024K
Macintosh Performa 5200/5210/5215/5220	4096K
Macintosh Performa 5260	4096K
Macintosh Performa 5300	4096K
Macintosh Performa 6100 Series	4096K
Macintosh Performa 62xx	4096K
Macintosh Performa 6300	4096K
Macintosh Performa 6320	4096K
Macintosh Performa 6400 series	4096K
Macintosh Performa 6360	4096K
Macintosh Performa 6290	4096K

Macintosh Quadra Models
Macintosh Quadra 605	1024K
Macintosh Centris/Quadra 610	1024K
Macintosh Quadra 630	1024K
Macintosh Centris/Quadra 650	1024K
Macintosh Quadra 700	1024K
Macintosh Quadra 800	1024K
Macintosh Quadra 900	1024K
Macintosh Quadra 950	1024K
Macintosh Centris/Quadra 660AV	1024K
Macintosh Quadra 840AV	2048K
Apple Workgroup Servers
Apple Workgroup Server 60	1024K
Apple Workgroup Server 80	1024K
Apple Workgroup Server 90	1024K
Apple Workgroup Server 95	1024K
Apple Workgroup Server 6150	4096K
Apple Workgroup Server 8150	4096K
Apple Workgroup Server 9150	4096K
Apple Workgroup Server 7250	4096K
Apple Workgroup Server 8550	4096K
Power Macintosh Models
Power Macintosh 4400 series	4096K
Power Macintosh 5200/75 LC	4096K
Power Macintosh 5260/100	4096K
Power Macintosh 5300/100 LC	4096K
Power Macintosh 5400 series	4096K
Power Macintosh 5500 series	4096K
Power Macintosh 6400 series	4096K
Power Macintosh 6500 series	4096K
Power Macintosh 6100 series	4096K
Power Macintosh 7100 series	4096K
Power Macintosh 7200 series	4096K
Power Macintosh 7300 series	4096K
Power Macintosh 7500/100	4096K
Power Macintosh 7600 series	4096K
Power Macintosh 8100 series	4096K
Power Macintosh 8500 series	4096K
Power Macintosh 8600 series	4096K
Power Macintosh 9500 series	4096K
Power Macintosh 9600 series	4096K
Power Macintosh G3	4096K
Power Macintosh G3 (Blue and White)	1024K
Macintosh PowerBook Models
Macintosh Portable	256K
Macintosh Backlit Portable	256K
PowerBook 100	256K
PowerBook 140	1024K
PowerBook 145	1024K
PowerBook 150	1024K
PowerBook 160	1024K
PowerBook 165c	1024K
PowerBook 170	1024K
PowerBook 180/180c	1024K
PowerBook Duo 210	1024K
PowerBook Duo 230	1024K
PowerBook Duo 250	1024K
PowerBook Duo 270c	1024K
PowerBook Duo 280/280c	1024K
PowerBook 520/520c	2048K
PowerBook 540/540c	2048K
PowerBook 1400	1024K
PowerBook Duo 2300 series	4096K
PowerBook 5300 series	4096K

Maximum size of ROM available

8 MB Flash EEPROM with Intel Platform Innovation Framework for EFI Plug and Play.

What is the reason for keeping ROM size smaller then RAM size?

Basically ROM has fixed data that is used in computer startup. After that there is no more use of it. It doesn’t have to store temporary data and startup information is very low in size.