Bootrom

The bootrom (called "SecureROM" by Apple) is the first significant code that runs on an iDevice. The bootrom is read-only. Finding exploits in the bootrom level is a big achievement since Apple won't be able to fix it without a hardware revision.

Old & New bootrom
Certain models, including the iPod touch (2nd generation) and iPhone 3GS, have different bootrom versions. These are most commonly referred to with the terms "old bootrom" and "new bootrom." These "new bootrom" devices were released after 9 September 2009 and have the 0x24000 Segment Overflow fixed. While the new bootrom revisions have an exploit, the exploit needs the assistance of a firmware-based exploit to achieve an untethered jailbreak.

You might also be looking for Apple's stage 2 bootloader, which also uses the "iBoot" name.

Usually also looking at the CPRV (Chip Revision) tag will also tell you whether the device is new unit or not also.

From the model number (iPod touch (2nd generation))
If the second character of your Model Number is "B" (e.g.- FB533, MB533, or PB533), your iPod has the old bootrom. If the second character is "C" (FC086, MC086 or PC086), your iPod has the new bootrom.

From the serial number (iPhone 3GS)
The third digit of the serial number identifies the year of manufacture (9=2009, 0=2010, 1=2011, 2=2012), while the fourth and the fifth indicate the week. There is a gray area between week 40 of 2009 (??940??????) and week 45 of 2009 (??945??????) where some devices have new bootrom whilst others have old bootrom. . Any iPhone made after Week 45 of 2009 (??945?????? and higher or ??0???????? serials) has the new bootrom.

Windows

 * 1) Connect Device & Enter DFU Mode
 * 2) Open Device Manager, find USB controller, subitem Apple Mobile Device USB Driver
 * 3) Right-Click & click Properties
 * 4) Go to Details tab & select Device Instance Path in the dropdown box
 * 5) The end of the info string will show the bootrom version

Mac OS X

 * 1) Connect Device & Enter DFU Mode
 * 2) Go to System Profiler, and under the Hardware category, go to USB, and click on Apple Mobile Device (DFU Mode)
 * 3) The end of the Serial Number string will show the bootrom version in brackets (ie: [iBoot-574.4])

Linux

 * 1) Make sure your distribution has usbutils installed. (most distributions have it by default)
 * 2) Connect Device & Enter DFU Mode
 * 3) In terminal, run sudo lsusb -v
 * 4) Find the line that says iSerial and your bootrom version will be at the end of the line.

Dumping the bootrom
You can use Bootrom Dumper Utility by pod2g to dump the bootrom on devices that are vulnerable to the Limera1n Exploit.

Bootrom Exploits

 * Pwnage 1.0 (Ramdisk + AppleImage2NORAccess) up to Rev.2
 * Pwnage 2.0 (DFU + Malformed Certificate) up to Rev.2
 * 0x24000 Segment Overflow up to 240.4/359.3
 * usb_control_msg(0xA1, 1) Exploit (also called "steaks4uce" exploit) only for 240.4 and 240.5.1
 * Limera1n Exploit up to 574.4
 * SHAtter up to 574.4

Revisions

 * Bootrom Rev.2 in S5L8900
 * Bootrom 240.4 in S5L8720 (old version only)
 * Bootrom 359.3 in S5L8920 (old version only)
 * Bootrom 240.5.1 in S5L8720 (new version only)
 * Bootrom 359.3.2 in S5L8920 (new version only)
 * Bootrom 359.5 in S5L8922
 * Bootrom 574.4 in S5L8930
 * Bootrom 838.3 in S5L8940
 * Bootrom 878.3 in S5L8942
 * Bootrom 1062.2 in S5L8945
 * Bootrom 1458.2 in S5L8947
 * Bootrom 1145.3 in S5L8950
 * Bootrom 1145.3.3 in S5L8955
 * Bootrom 1704.10 in S5L8960 and S5L8965
 * Bootrom 1992.0.0.1.19 in T7000
 * Bootrom 1991.0.0.2.16‎ in T7001
 * unknown S7002
 * Bootrom 2234.0.0.3.3 in S8000
 * Bootrom 2234.0.0.2.22 in S8003

S5L8900, used in the iPhone, iPod touch, and iPhone 3G
see also VROM (S5L8900)
 * Bootrom Rev.2

S5L8720, used in the iPod touch (2nd generation)

 * Bootrom 240.4 "old bootrom"
 * Bootrom 240.5.1 "new bootrom"

S5L8920, used in the iPhone 3GS

 * Bootrom 359.3 "old bootrom"
 * Bootrom 359.3.2 "new bootrom"

S5L8922, used in the iPod touch (3rd generation)

 * Bootrom 359.5

S5L8930, used in the iPad, iPhone 4, Apple TV (2nd generation), and iPod touch (4th generation)

 * Bootrom 574.4

S5L8940, used in the iPad 2 and iPhone 4S

 * Bootrom 838.3

S5L8942, used in the iPad 2 (iPad2,4), Apple TV (3rd generation) (AppleTV3,1), iPod touch (5th generation), and iPad mini

 * Bootrom 878.3

S5L8945, used in the iPad (3rd generation)

 * Bootrom 1062.2

S5L8947, used in the Apple TV (3rd generation) (AppleTV3,2)

 * Bootrom 1458.2

S5L8950, used in the iPhone 5 and iPhone 5c

 * Bootrom 1145.3

S5L8955, used in the iPad (4th generation)

 * Bootrom 1145.3.3

S5L8960/S5L8965, used in the iPhone 5s, iPad Air, iPad mini 2, and iPad mini 3

 * Bootrom 1704.10

T7000, used in the Apple TV (4th generation), iPad mini 4, iPhone 6, iPhone 6 Plus, and iPod touch (6th generation)

 * Bootrom 1992.0.0.1.19

T7001, used in the iPad Air 2

 * Bootrom 1991.0.0.2.16

S7002, used in the Apple Watch (1st generation)

 * unknown

S8000, used in the iPhone 6s, iPhone 6s Plus and iPhone SE

 * Bootrom 2234.0.0.3.3

S8001, used in the iPad Pro

 * Bootrom 2481.0.0.2.1

S8003, used in the iPhone 6s, iPhone 6s Plus and iPhone SE

 * Bootrom 2234.0.0.2.22

T8002, used in the Apple Watch Series 1 and Apple Watch Series 2

 * Bootrom 2651.0.0.1.31

T8010, used in the iPhone 7 and iPhone 7 Plus

 * Bootrom 2696.0.0.1.33