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(CNN) —  

It sounds outdated, but Cyber Monday is still a thing.

The day of online sales was invented by retailers in the early days of the internet.

It made sense because people had poky dial-up connections at home and faster ones at work. Plus everyone’s feet were tired from all that schlepping through the mall all weekend.

Now of course we all shop a lot online and on apps, whenever we want. And there’s not really a difference between online stores and physical ones. Even Amazon, which effectively invented online shopping, has storefronts.

But that doesn’t stop companies from doubling down on sales on Monday.

Cyber Monday 2018 is expected to be the largest online shopping day in US history, generating a whopping $7.8 billion in sales, a more than 17% increase from the previous year, according to Adobe Analytics, which tracks online sales.

The Gap, which is struggling, is offering 50% off every item, plus an additional 10% on online specials and free shipping. Kohl’s (KSS) is offering 20% off of all items between Saturday November 24 and Wednesday November 28, in what it’s billed as Cyber Week. Shoppers there can also get $15 Kohl’s cash for every $50 spent.

Best Buy (BBY) is offering discounts on a number of electronics items like the Microsoft Xbox, Samsung Galaxy phones and 4K Blu Ray players.

On top of doorbuster deals, Target is offering an additional 15% off all orders made on Monday.

JCPenney (JCP) is giving an extra 30% off orders more than $100.

Walmart is expected to discount a selection of electronics like phones, laptops and gaming systems. Amazon is offering a series of deals on a range of items. Amazon’s discounts will last until December 1.

A strong US economy, healthy consumer spending and low gas prices could give retailers a lift this holiday stretch. Sales during the holidays will be up between 4.3% and 4.8% compared to 2017, the National Retail Federation predicts.

Nearly every retailer taking part is offering free shipping, which can cost a bundle.

The problem is that discounting is killing the bottom line at many stores.

Target’s (TGT) stock price plunged last week when it said that costs were rising, in part from fulfilling online orders.

Walmart (WMT)is struggling with a similar problem. It offers highly popular items online, but those sales carry lower profit margins. Fluctuating shipping costs can eat into those margins.

“The process takes time, and we’re making progress,” CEO Doug McMillon has said.

Every retailer wants to win on Cyber Monday.

Struggling companies like JCPenney and Victoria’s Secret have to prove that they can still compete in a promotion-heavy environment.

Kohl’s, Macy’s, TJMaxx, and Best Buy have all had stellar 2018 campaigns, and they don’t want a letdown on Cyber Monday.

Walmart and Target are attempting to show investors that they are serious online players, capable of going up against Amazon on the busiest day of the year.

There’s even pressure on Amazon this Cyber Monday.

The company’s stock price tumbled in October when its holiday forecast disappointed Wall Street.