Job File Table

Job File Table

The Job File Table (JFT) is a DOS data structure in the Program Segment Prefix (PSP). It starts at PSP offset 0x18 and is 20 bytes long. For each open file handle, DOS stores the index into the System File Table (SFT). A file handle that is returned by open, _open and other similar functions is simply an index into the JFT where DOS stored the SFT entry index for the file or device that the program opened.

When a program starts, the first 5 entries in the JFT are preconnected to the standard devices. All other handles are marked as closed by setting the value of the entry to 0xFF.The standard devices are initialised as follows Handle Description 0 standard input 1 standard output 2 standard errorHandles 0-2 are connected to the console device. During program execution they can get modified (closed, redirected) like any other handle.

Because the size of the JFT in the PSP is limited to 20 bytes, you could originally only open 15 files (20-5 standard devices). As of MS-DOS 2.0 the Extended Job File Table was introduced, which allowed to open up to 254 files.

As of MS-DOS 3.30 the size of the JFT can be modified with a call to INT 21h, 67h.


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Table saw — A table saw, equipped for cutting large pieces of sheet stock. Other names Sawbench Classification Power tool Manufacturer Bosch, Makita …   Wikipedia

  • Table of keyboard shortcuts — In computing, a keyboard shortcut is a sequence or combination of keystrokes on a computer keyboard which invokes commands in software. Some keyboard shortcuts require the user to press a single key or a sequence of keys one after the other.… …   Wikipedia

  • STL (file format) — Infobox file format name = STL icon = caption = extension = .stl mime = type code = uniform type = magic = owner = 3D Systems released = latest release version = latest release date = genre = Stereolithography container for = contained by =… …   Wikipedia

  • Hands Across the Table — Infobox Film name = Hands Across the Table image size = caption = director = Mitchell Leisen producer = E. Lloyd Sheldon writer = Norman Krasna Based on a story by Viña Delmar narrator = starring = Carole Lombard Fred MacMurray music =… …   Wikipedia

  • Program Segment Prefix — (рус. Префикс программного сегмента, PSP) структура данных, которая используется в операционных системах семейства DOS и CP/M для сохранения состояния компьютерных программ. PSP в DOS имеет следующую структуру: Offset (Смещение) Size (Размер)… …   Википедия

  • Program Segment Prefix — Als Programmsegmentpräfix (engl. Program Segment Prefix, PSP) bezeichnet man die ersten 256 Byte eines von MS DOS geladenen Programmes. Das PSP ist nicht in den ausführbaren Exe oder Com Dateien enthalten, sondern wird beim Laden des Programmes… …   Deutsch Wikipedia

  • JFT — Die Abkürzung JFT bedeutet: Job File Table Jugend Freizeit Ticket Jugendfreizeittreff Juristenfakultätentag just for today (dt. nur heute) zum sofortigen Verbrauch bestimmt oder als Marketingmethode eingesetzt Andere Bezeichnungen:… …   Deutsch Wikipedia

  • JFT — abbr. Job File Table …   Dictionary of abbreviations

  • JFT — abbr. Job File Table (DOS) …   United dictionary of abbreviations and acronyms

  • Abkürzungen/Computer — Dies ist eine Liste technischer Abkürzungen, die im IT Bereich verwendet werden. A [nach oben] AA Antialiasing AAA authentication, authorization and accounting, siehe Triple A System AAC Advanced Audio Coding AACS …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”